Use the new URL for docs preview link (#60893)
Summary:
This is all set up on CloudFront now with a custom domain, so we don't need the long default cloudfront domain anymore
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60893
Reviewed By: malfet
Differential Revision: D29437300
Pulled By: driazati
fbshipit-source-id: 6f5ffd1b10c5167b0022b7e64b2164508624ca91
